The present invention refers to a method for cutting blocks of granite, marble and other stone materials, conglomerate, concrete and similar.
The invention refers likewise to an oscillating frame machine, comprising a plurality of parallel blades provided with diamond segments, suitable for cutting stone blocks or similar materials into flat slabs, even of large dimensions.
Normally Indeed the stone blocks are cut in large slabs, using multi-blade gangsaws, or directly in unitary small sizes, using diamond disk sawing machines.
While an horizontal multi-blade gangsaw is able to cut slabs high up to 2 meters, a disk sawing machine can cut a total height not much greater then the third of the diameter of the same disk, which therefore should have an impossible diameter of five meters for cutting a similar height of slab.
Moreover in order to have supports and diamond segments of analogous thickness, and therefore analogous losses of scrap material, it is necessary to compare a gangsaw blade with a disk having a diameter of only 600 millimeters, which allows to cut a slab height of only 200 millimeters, a tenth of the height that can be cut by a blade.
A disk suitable for cutting one meter in height has a diameter of more than 2.5 meters and diamond segments having a thickness of 12 millimeters in opposition to 5.5 millimeters of a diamond blade. The scrap material is therefore double, the cost of the tool is higher and the energy used during cutting is greater. The diamond disk has however a higher cutting speed, at least 10 times greater than that of a gangsaw blade.
The manufacturing process and consequent needs normally lead operators to chose one or the other cutting system.
The present state of the art permits the use of diamond segments whether in disks for cutting marble or in those for cutting granite. On the contrary the diamond blades are used only for cutting marble. For cutting granite are used steel blades transporting against the stone to be cut scattered grit carried by the washing water and mixed with additives. The cuts made in the block are 8/10 mm large and therefore 30-60% larger then the cuts of a diamond blade.
Consequently the cut with gangsaws having alternate rectilinear motion, although using similar machines for xe2x80x9csoftxe2x80x9d calcareous materials, situated under level 4 of Mohs scale, and for xe2x80x9chardxe2x80x9d siliceous materials, which can exceed level 8, shows operating management substantially different and also installed power and cutting scraps very different, connected to the possibility of using or not blades provided with diamond segments.
Moreover the fact of using ferrous grit for cutting by means of multi-blade gangsaws granite and hard stones lets into the process and washing water, and therefore into the working environment, large quantities of iron oxide that contaminates and stains the materials. As a consequence the cutting operations of marble and granite, that are the first, and sometimes the only, in the manufacturing process of a factory, must be maintained separated in order to separate the circulation of processing waters.
First attempts of cutting granite with diamond blade gangsaws have been made during first seventies, when were introduced diamond gangsaws for cutting marble. IN these last 25 years, while the use of diamond gangsaws for cutting marble and soft stones was consolidating, attempts for cutting granite and other hard stones with diamond blade gangsaws went on but without relevant successes.
Among the causes of these unprofitable attempts are the following:
The hardness of granites and other hard stones, much more similar to that of natural or synthetic diamond than to that of calcareous materials and soft stones.
The reciprocating of blades that prevents the formation of a stable support for the single diamond granule, as the one that grows in the diamond segment when it moves always in the same direction. Since the segments move in two directions the diamond tends to oscillate and separate more easily from the binder and it is ejected prematurely.
The inadequate contact linear velocity of the diamond segments of the gangsaw blade, much lower then that of a diamond disk.
The inefficient drainage of scrap material and the consequent stay and entrainment in the two directions of the material counterabrasive for diamond made by granules of abraded material, having a hardness not much lower then that of diamond.
The attempts made till now for cutting granite by means of gangsaws having diamond blades did not lead to construction of diamond gangsaws technically efficient and economically valid for cutting granite.
In the patent U.S. Pat. No. 2,554,678 it is disclosed a gangsaw which uses a set of blades in a frame that is eccentrically connected to a couple of wheels having discordant movement, that transfer to the blades a reciprocating movement leading to an elliptic movement on a variable slope.
In the published documents EP 0 002 265 and WO 92/22408 are disclosed vertical gangsaws in which the blade frame moves along an elliptic path therefore carrying the blades in contact with the material to be cut during only one direction of the reciprocating movement. In order to increase the speed of the tools the gangsaws have been lightened and they are necessarily of the vertical type, with shortened blades.
The practical results of these solutions are not known but it can be noted that, while the gangsaw disclosed in document EP 0 002 265 has an operation that subjects the tools to irregular and not foreseeable loads and wears, the constructive criteria of the second gangsaw, disclosed in document WO 92/22408, do not allow to attack the material with adequate power and abrasive capability.
The document WO 92/22408 starts from the assumption, correct but over-estimated, that it is necessary to use specific diamond tools for the five hardness classes and cutting difficulties in which granites are classified.
Referring to cutting of calcareous stone materials using diamond gangsaws the practice confirmed that a blade having diamond sectors purposely designed and manufactured for a specific material can have optimal drops in that material. For example on travertine, that has a perforated structure, weak and very dry, that reduces stresses and facilitates drainage of abraded material, as it can be absorbed by holes, have been obtained drops of 50 cm/h and more. It is therefore justifiable that firms working exclusively on travertine use specific blades.
However the qualities of marble on the market are hundreds and it is not possible for a firm to equip itself with special blades for every type of marble and neither with special blades for families of materials. In this field indeed are used universal blades and the gangsaw operation is so programmed that, after cutting a block of material that gums the blades, is cut a more abrasive and dry block that dresses them. The drops, the yield and average costs obtained are considered acceptable. If we also consider the greater hardness and different structure of granite, the logic should be the same and lead to the construction of universal diamond blades also for granite.
As regards granite, it is commonly believed that it cannot be cut in a cost-effective way using a diamond gangsaw because the speed of the tool is too low. The optimal speed, given by manufacturers of diamond tools for cutting granite, is in fact approximately 20 m/s, while the medium possible speed on a gangsaw is 1 m/s. Therefore it should not be possible to cut granite using a diamond gangsaw because the possible linear speed of the tool is not sufficient. But if this would be a valid reason it would remain to explain why diamond gangsaws operate correctly on marble, where the suggested correct speed is double, more then 40 m/s. And also why the diamond cost per square meter cut is substantially the same for a disk, having optimal tip speed, and for a blade that operates at not constant speed, with a wrong average speed, equal to approximately 3% of optimal speed.
The truth is that the high tip or linear speed of the diamond tool, which is however difficult to increase in gangsaws because of relevant masses reciprocally moved, is not determinant either for the possibility of cutting material or for defining the final cost of the operation, wherein the wear of the tool is determinant. On the contrary it is a most important factor to obtain an efficient drainage for the material abraded during cutting, in order to eliminate or minimise the counterabrasion effect on diamond sectors.
Diamond gangsaws currently used for cutting marbles and soft stones are machines having a very simple operation in which the only parameters controllable and changeable during operation are the drop, i.e. the approaching speed between blades and material or vice versa, and the quantity of lubricating water for the cut and the drainage of abraded material. In these gangsaws the blades and the diamond sectors are always in contact with the material to be cut.
A first object of the present invention it is therefore to provide a cutting method more efficient, cost-effective and speedy for marble and soft stones and to allow, using different tools, to cut blocks of granite or hard stone by means of a gangsaw, overcoming the defects of the prior art.
Another object of the present invention is to provide a diamond gangsaw having particular functions that allow to cut efficiently every stone material and analogous materials, even hard, using limited power and limited machining scraps.
The above objects of the present invention are reached from a method and a frame cutting machine as claimed in the accompanying claims.
According to the invention the method for cutting blocks of stone, by means of a frame provided with diamond sector blades, comprises, besides a reciprocal approaching movement between blades and block and a periodical reciprocating movement of the blades, also a cyclic movement of approaching and moving away of the blades relative to the block and a hunting movement of the blade frame.
Thanks to the presence of the cyclic movement of approaching and moving away of the blades relative to the block, the gangsaw according to the invention has better cutting characteristics in respect to prior art and at allows, thanks to the moving away of the blades from the block, to clear regularly the cutting groove from the abraded material.